Ultrafast Insulator-Metal Phase Transition in VO2 Studied by Multiterahertz Spectroscopy

The ultrafast photoinduced insulator-metal transition in VO2 is studied at different temperatures and excitation fluences using multi-THz probe pulses. The spectrally resolved mid-infrared response allows us to trace separately the dynamics of lattice and electronic degrees of freedom with a time resolution of 40 fs. The critical fluence of the optical pump pulse which drives the system into a long-lived metallic state is found to increase with decreasing temperature. Under all measurement conditions we observe a modulation of the eigenfrequencies of the optical phonon modes induced by their anharmonic coupling to the coherent wave packet motion of V-V dimers at 6.1 THz. Furthermore, we find a weak quadratic coupling of the electronic response to the coherent dimer oscillation resulting in a modulation of the electronic conductivity at twice the frequency of the wave packet motion. The findings are discussed in the framework of a qualitative model based on an approximation of local photoexcitation of the vanadium dimers from the insulating state.Comment: 10 pages, 8 figures submitted to Physical Review

Quantum interference between charge excitation paths in a solid state Mott insulator

The competition between electron localization and de-localization in Mott insulators underpins the physics of strongly-correlated electron systems. Photo-excitation, which re-distributes charge between sites, can control this many-body process on the ultrafast timescale. To date, time-resolved studies have been performed in solids in which other degrees of freedom, such as lattice, spin, or orbital excitations come into play. However, the underlying quantum dynamics of bare electronic excitations has remained out of reach. Quantum many-body dynamics have only been detected in the controlled environment of optical lattices where the dynamics are slower and lattice excitations are absent. By using nearly-single-cycle near-IR pulses, we have measured coherent electronic excitations in the organic salt ET-F2TCNQ, a prototypical one-dimensional Mott Insulator. After photo-excitation, a new resonance appears on the low-energy side of the Mott gap, which oscillates at 25 THz. Time-dependent simulations of the Mott-Hubbard Hamiltonian reproduce the oscillations, showing that electronic delocalization occurs through quantum interference between bound and ionized holon-doublon pairs.Comment: 4 figures and supplementary informatio

Soft landing of size selected clusters in rare gas matrices

Soft landing of mass selected clusters in rare gas matrices is a technique used to preserve mass selection in cluster deposition. To prevent fragmentation upon deposition, the substrate is covered with rare gas matrices to dissipate the cluster kinetic energy upon impact. Theoretical and experimental studies demonstrate the power of this technique. Besides STM, optical absorption, excitation, and fluorescence experiments, x-ray absorption at core levels can be used as a tool to study soft landing conditions, as will be shown here. X-ray absorption spectroscopy is also well suited to follow diffusion and agglomeration of clusters on surfaces via energy shifts in core level absorption

Probing photo-induced melting of antiferromagnetic order in La0.5Sr1.5MnO4 by ultrafast resonant soft X-ray diffraction

Photo-excitation in complex oxides1 transfers charge across semicovalent bonds, drastically perturbing spin and orbital orders2. Light may then be used in compounds like magnetoresistive manganites to control magnetism on nanometre lengthscales and ultrafast timescales. Here, we show how ultrafast resonant soft x-ray diffraction can separately probe the photo-induced dynamics of spin and orbital orders in La0.5Sr1.5MnO4. Ultrafast melting of CE antiferromagnetic spin order is evidenced by the disappearance of a (1/4,1/4,1/2) diffraction peak. On the other hand the (1/4,1/4,0) peak, reflecting orbital order, is only partially reduced. Cluster calculations aid our interpretation by considering different magnetically ordered states accessible after photo-excitation. Nonthermal coupling between light and magnetism emerges as a primary aspect of photo-induced phase transitions in manganites.Comment: 7 pages manuscript, 4 figure

House Dust Mite Exposure Causes Increased Susceptibility of Nasal Epithelial Cells to Adenovirus Infection

Adenovirus (AdV) infections in the respiratory tract may cause asthma exacerbation and allergic predisposition, and the house dust mite (HDM) may aggravate virus-induced asthma exacerbations. However, the underlying mechanisms of whether and how AdV affects asthmatic patients remains unclear. To address this question, we investigated nasal epithelial cells (NAEPCs) derived from a pediatric exacerbation study cohort for experimental analyses. We analyzed twenty-one different green-fluorescent protein- and luciferase-tagged AdV types in submerged 2D and organotypic 3D cell culture models. Transduction experiments revealed robust transduction of AdV type 5 (AdV5) in NAEPCs, which was associated with an increased uptake of AdV5 in the presence of HDM. In healthy and asthmatic NAEPCs exposed to HDM before infection, we observed a time- and dose-dependent increase of AdV5 uptake associated with upregulation of entry receptors for AdV5. Furthermore, electron microscopic and histologic analyses of 3D cell cultures revealed an impairment of the respiratory cilia after HDM exposition. This ex vivo pilot study shows the impact of AdV infection and HDM exposition in a primary cell culture model for asthma

Increased immunogenicity of surviving tumor cells enables cooperation between liposomal doxorubicin and IL-18

<p>Abstract</p> <p>Background</p> <p>Liposomal doxorubicin (Doxil) is a cytotoxic chemotherapy drug with a favorable hematologic toxicity profile. Its active drug, doxorubicin, has interesting immunomodulatory properties. Here, the effects of Doxil on surviving tumor cell immunophenotype were investigated.</p> <p>Methods</p> <p>Using ID8 murine ovarian cancer cells, the immunomodulatory effects of Doxil were studied by measuring its impact on ovarian cancer cell expression of MHC class-I and Fas, and susceptibility to immune attack <it>in vitro</it>. To evaluate the ability of Doxil to cooperate with cancer immunotherapy, the interaction between Doxil and Interleukin 18 (IL-18), a pleiotropic immunostimulatory cytokine, was investigated <it>in vivo </it>in mice bearing ID8-Vegf tumors.</p> <p>Results</p> <p>While Doxil killed ID8 tumor cells in a dose-dependent manner, tumor cells escaping Doxil-induced apoptosis upregulated surface expression of MHC-I and Fas, and were sensitized to CTL killing and Fas-mediated death <it>in vitro</it>. We therefore tested the hypothesis that the combination of immunotherapy with Doxil provides positive interactions. Combination IL-18 and Doxil significantly suppressed tumor growth compared with either monotherapy <it>in vivo </it>and uniquely resulted in complete tumor regression and long term antitumor protection in a significant proportion of mice.</p> <p>Conclusion</p> <p>These data demonstrate that Doxil favorably changes the immunophenotype of a large fraction of the tumor that escapes direct killing thus creating an opportunity to expand tumor killing by immunotherapy, which can be capitalized through addition of IL-18 <it>in vivo</it>.</p